Hydrogen peroxide is useful as an indispensable reagent in the manufacture of foods, medicines, pulp, fiber, semiconductors, etc., and has been heretofore been synthesized by an anthraquinone method.
Heretofore, in a power plant or factory using sea water as cooling water, it has been the practice to directly electrolyze sea water to produce hypochlorous acid which is effectively used to prevent the attachment of organisms onto the inner wall of a condenser. However, because hypochlorous acid itself and organic chlorine compounds or chlorine gas produced by the decomposition thereof are harmful to the environment, hypochlorous acid should not be discharged as such. The regulation of hypochlorous acid discharge has intensified.
On the other hand, it has been reported that hydrogen peroxide, if added to the foregoing cooling water, prevents the attachment of organisms. It has also been reported that the addition of hydrogen peroxide advantageously maintains the quality of water in a fish farm. Furthermore, hydrogen peroxide decomposes to only water and oxygen, which are harmless and cause no problems in environmental health.
However, hydrogen peroxide is unstable and thus cannot be stored over an extended period of time. For this reason, and from the standpoint of safety and environmental protection during transportation, the demand for an on-site type apparatus for the production of hydrogen peroxide has grown.
In order to meet this demand, the study of synthesis methods for the production of hydrogen peroxide by reduction with oxygen gas has heretofore been reported. U.S. Pat. No. 3,693,749 proposes several kinds of electrolytic apparatus. U.S. Pat. No. 4,384,931 discloses an electrolytic process using an ion-exchange membrane as a process for the production of an alkaline aqueous solution of hydrogen peroxide. Furthermore, U.S. Pat. No. 3,969,201 discloses a hydrogen peroxide production apparatus comprising a carbon negative electrode and an ion-exchange membrane which are three-dimensional. However, this proposal is disadvantageous in that the resulting aqueous solution of hydrogen peroxide has a high alkali concentration as compared with the hydrogen peroxide concentration and thus is restricted in terms of its use. Moreover, U.S. Pat. Nos. 4,406,758, 4,891,207 and 4,457,953 disclose a process for the production of hydrogen peroxide using a porous membrane material and a porous hydrophobic carbon negative electrode. These processes are disadvantageous in that the amount and rate of migration of electrolytic solution from the positive electrode chamber to the negative electrode chamber is difficult to control, thus complicating the operation. Furthermore, in the Journal of The Electrochemical Society, Vol. 130, pp. 1,117--(1983), a process is proposed which comprises supplying sulfuric acid to a middle chamber between a cation-exchange membrane and an anion-exchange membrane to stably obtain an acidic solution of hydrogen peroxide. Moreover, it is reported in "Denki Kagaku (Electrochemistry)", Vol. 57, page 1073, 1989, that the use of a membrane electrode connection as an anode makes it possible to improve the properties of the system. However, this process is economically disadvantageous in that the power supply is expensive. All of these processes involve the efficient production of hydrogen peroxide in an atmosphere of an alkaline aqueous solution. Therefore, these processes require the use of an alkaline component as a raw material. This alkaline component is difficult to transport. Thus, a satisfactory hydrogen peroxide production apparatus has heretofore not been provided.
On the other hand, as discussed above, from the standpoint of problems arising from the direct electrolysis of sea water, the use of hydrogen peroxide in the treatment of sea water has been extensively studied as an economically favorable approach. The conventional process for the production of hydrogen peroxide by electrolysis of sea water is further disadvantageous in that it involves the addition of chemicals to sea water, thereby causing another environmental pollution problem. In the case where hydrogen peroxide is also used to treat sea water, and if an alkaline aqueous solution is separately prepared and added to the sea water, similar environmental pollution occurs.
In order to eliminate these difficulties, the inventors proposed a process for the production of hydrogen peroxide which comprises subjecting sea water to salt separation to obtain an alkaline aqueous solution and an acidic aqueous solution, and then producing hydrogen peroxide from the alkaline aqueous solution, characterized in that the alkaline aqueous solution thus used is neutralized with the acidic aqueous solution. This process eliminates the need for externally adding chemicals and thus causes little or no environmental pollution. This process also requires an extremely small amount of power, and thus is an ideal production process. However, this production process is disadvantageous in that while the electrolysis actually continues, it is difficult to remove an alkaline earth metal such as calcium and magnesium contained in sea water under stable conditions. This process is also disadvantageous in that the alkali concentration of the alkaline aqueous solution for the production of hydrogen peroxide cannot be adequately increased.